A solution and solid state study of niobium complexes University of ...

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Chapter 2 Figure 2.11: Structure of [Sr2Nb2O(thd)3(OEt)9(EtOH)3]. Figure 2.12: Structure of [Sr2Nb2O(thd)3(O n Pr)9( n PrOH)3. 29
2.7 Alkoxides Chapter 2 Specific knowledge of the nature of the species formed in alcoholic solutions of metal ions is essential for the manufacture of the final product. Metal alkoxides have the general formula M(OR)x, where M is the metal with a valence x and O is the oxygen atom that connects the alkyl group (R) to the metal at each valence site. Metal alkoxides are usually very reactive species due to the presence of the electronegative alkoxy groups that make the metal atoms susceptible to nucleophilic attack. The properties of metal alkoxides are mainly determined by the shape and size of the alkyl group (R) as well as by the stereochemistry, valency, atomic radius and coordination number of the metal. Based on the high electronegativity of oxygen, the M-OR bonds are expected to possess fundamental ionic character. According to Bradley’s concept, 70 alkoxides with the lower primary or secondary alkyl groups have a strong tendency towards polymerization, creating coordination polymers [M(OR)x]n (where n is the degree of polymerization). The magnitude of polymerization is dependent on the following factors: 71 Aggregation increases as the metal atom becomes more electron deficient. The larger the size of the metal atom, the greater the tendency to increase the degree of association by forming alkoxo bridges. The steric effects of the alkyl substituents. They inhibit aggregation with an increase in steric demand and have been found to be of greater importance than the electronic nature of the substituents in determining the final extent of aggregation. 2.7.1 Preparation of Metal alkoxides Various methods are available for the preparation of metal alkoxides. The choice of synthesis depends on the ionisation energy of the metal. The less electronegative 70 D. C. Bradley, Nature, 182, 1211, 1958. 71 D. C. Bradley, R. C. Mehrotra, D. P. Gaur, Metal Alkoxides, Academic Press, London, 1978. 30
Page 1 and 2: A solution and solid state study of
Page 3 and 4: Table of contents Abbreviations and
Page 5 and 6: 3.4 Infrared Spectroscopy (IR) ....
Page 7 and 8: Abbreviations and Symbols Abbreviat
Page 9 and 10: Abstract 93 Nb NMR was successfully
Page 11 and 12: Opsomming 93 Nb KMR is met sukses g
Page 13 and 14: Chapter 1 metals. 3 Due to Wollasto
Page 15 and 16: Synopsis... 2. Literature Review of
Page 17 and 18: Chapter 2 Niobium resembles tantalu
Page 19 and 20: 2.1.2 Uses Chapter 2 Niobium has a
Page 21 and 22: 2.2 Separation of Nb and Ta 2.2.1 M
Page 23 and 24: Chapter 2 Buachuang et al. 16 repor
Page 25 and 26: Chapter 2 Niobium oxide surfaces ex
Page 27 and 28: 2.4.6 Water absorption Chapter 2 Th
Page 29 and 30: Chapter 2 been reported in literatu
Page 31 and 32: Chapter 2 containing niobium as the
Page 33 and 34: Chapter 2 conclusions, with regard
Page 35 and 36: Chapter 2 Figure 2.5: Structure of
Page 37 and 38: 2.6.3.3 [NbCl3O(ttbd) - ] Chapter 2
Page 39: Chapter 2 (a) (b) Figure 2.10: Stru
Page 43 and 44: Chapter 2 Reactions of dialkylamid
Page 45 and 46: Chapter 2 other NbCl5-x(OMe)x produ
Page 47 and 48: Chapter 2 In 1991 Lee et al. 83 pub
Page 49 and 50: EtO EtO EtO EtO Cl Nb Cl Cl Nb Cl R
Page 51 and 52: Chapter 2 The hemicarbonate formed
Page 53 and 54: Synopsis... 3. Synthesis and Charac
Page 55 and 56: Chapter 3 with γ = magnetogyric ra
Page 57 and 58: Chapter 3 electromagnetic spectrum
Page 59 and 60: 3.5.1 Bragg’s law Chapter 3 Bragg
Page 61 and 62: 3.5.3 ‘Phase problem’ Chapter 3
Page 63 and 64: Chapter 3 A = ∑ ε cl (3.14) In
Page 65 and 66: Chapter 3 t1/2 = 54 = . 3.7 Sy
Page 67 and 68: 3.7.2.4 Synthesis of [NbCl4(acac)]:
Page 69 and 70: 4. Crystallographic Synopsis... Cha
Page 71 and 72: Chapter 4 packages 2 respectively.
Page 73 and 74: Chapter 4 4.3 Crystal Structure of
Page 75 and 76: Chapter 4 longer bonds (C1-C2, C2-C
Page 77 and 78: Chapter 4 Figure 4.5: Packing of [N
Page 79 and 80: Chapter 4 Figure 4.7: Molecular str
Page 81 and 82: Chapter 4 Table 4.5: Selected bond
Page 83 and 84: Chapter 4 Figure 4.11: Molecular st
Page 85 and 86: Chapter 4 Figure 4.12: The phacac p
Page 87 and 88: Chapter 4 Table 4.9: Hydrogen bonds
Page 89 and 90: Chapter 4 According to our knowledg
Page 91 and 92:
5.2 Experimental procedures 5.2.1 K
Page 93 and 94:
Chapter 5 corresponds to one specie
Page 95 and 96:
5.3 Results and Discussion 5.3.1 Pr
Page 97 and 98:
Chapter 5 Figure 5.5: Typical UV/Vi
Page 99 and 100:
5.3.3 Derivation of the rate law Ch
Page 101 and 102:
Chapter 5 The Stopped-flow data (fa
Page 103 and 104:
Chapter 5 Figure 5.9: Eyring plot,
Page 105 and 106:
Chapter 5 However, more information
Page 107 and 108:
Chapter 6 second reaction entailed
Page 109 and 110:
Appendix A Table 1.3: Bond angles (
Page 111 and 112:
Appendix A A 2 Supplementary Data f
Page 113 and 114:
Appendix A C(16)-H(16B) 0.96 C(16)-
Page 115 and 116:
Appendix A O(7)-C(10)-C(11) 123.6 (
Page 117 and 118:
Appendix A H(18E)-C(18B)-H(18F) 109
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Appendix A H(18F) 6243 6605 575 75
Page 121 and 122:
Appendix A Table 3.3: Bond angles (
Page 123 and 124:
Appendix A Table 3.4: Anisotropic d
Page 125:
Appendix B Appendix B B 1 Supplemen
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A solution and solid state study of niobium complexes University of ...

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